Frame Structure for Work Vehicle

ABSTRACT

A work vehicle comprising a pair of left and right wheels; a vehicle body frame supported at least partially by the pair of left and right wheels; and a suspension provided between the pair of left and right wheels and the vehicle body frame, the suspension being a five-linkage type rigid axle suspension including: a pair of left and right upper arms and a pair of left and right lower arms for positioning the pair of left and right wheels in the longitudinal direction of the vehicle body, a lateral rod for positioning the pair of left and right wheels in the lateral direction of the vehicle body, a pair of left and right coil springs for absorbing shocks from the road, and a pair of left and right dampers for controlling the movements of the pair of left and right coil springs. An auxiliary frame is further provided for supporting the pair of left and right wheels, an engine, and a transmission device, wherein the auxiliary frame is suspended on the vehicle body frame via the suspension.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to frame structure for a work vehicle inwhich a vehicle body frame is provided with suspension for suspending apair of left and right vehicle wheels.

2. Description of the Related Art

In one example of a vehicle body structure for a work vehicle such as isdescribed above, the engine is mounted via a plurality of anti-vibrationrubber pads to an engine mounting frame connected to a main frame, atransmission case and a hydraulic continuously variable transmission areinstalled in a transmission support frame connected to the main frame,and a pair of left and right rear wheels driven by power from the engineis suspended on the main frame via a leaf spring type of rigid axlesuspension (for example, see Japanese Laid-open Patent Application No.2004-50954).

In the configuration described above, since the left and right rearwheels driven by power from the engine are suspended via the suspensionon the vehicle body frame containing the engine and the transmissionapparatus, the left and right rear wheels become displaced in relationto the engine and the transmission apparatus when the suspension reducesvibrations or shocks from the road. Therefore, the system fortransmitting power to the left and right tear wheels must be providedwith universal couplings or the like that allow displacement in the leftand right rear wheels in relation to the engine and the transmissionapparatus.

Since the engine is mounted in the vehicle body frame via a plurality ofanti-vibration rubber pads, the power transmission system running fromthe engine to the transmission apparatus must be provided with universalcouplings or the like that allow relative displacement between theengine and the transmission apparatus.

In other words, attempting to create a smoother ride by reducingvibrations or shocks from the road with a suspension and by absorbingengine vibrations with anti-vibration rubber pads has led to morecomplex configurations and higher costs due to installing a plurality ofuniversal couplings or the like.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a work vehicle havingan improved frame in which the configuration is simplified and a smoothride can be ensured.

The work vehicle according to an aspect of the present inventioncomprises:

a pair of left and right wheels;

a vehicle body frame supported at least partially by the pair of leftand right wheels; and

a suspension provided between the pair of left and right wheels and thevehicle body frame, the suspension being a five-linkage type rigid axlesuspension including:

-   -   a pair of left and right upper arms and a pair of left and right        lower arms for positioning the pair of left and right wheels in        the longitudinal direction (or fore-and-aft direction) of the        vehicle body;        -   a lateral rod for positioning the pair of left and right            wheels in the lateral direction of the vehicle body;        -   a pair of left and right coil springs for absorbing shocks            from the road;        -   a pair of left and right dampers for controlling the            movements of the pair of left and right coil springs; and        -   an auxiliary frame for supporting the pair of left and right            wheels, an engine, and a transmission device, wherein the            auxiliary frame is suspended on the vehicle body frame via            the suspension.

According to this aspect, the engine and the transmission devices areinstalled along with the left and right front wheels on the auxiliaryframe suspended via the suspension on the vehicle body frame, wherebythe engine and the transmission devices are displaced integrally alongwith the left and right wheels in relation to the vehicle body framewhen the suspension reduces vibrations or shocks from the road.Therefore, there is no need to provide the power transmission system forthe left and right wheels with universal couplings or the like so as toallow the left and right wheels to be displaced in relation to theengine and the transmission devices.

Therefore, it is possible to simplify the configuration by reducing thenumber of components and to ensure a smooth ride in which vibrations orshocks from the road are reduced and engine vibrations are absorbed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall side view of a multipurpose work vehicle;

FIG. 2 is a schematic plan view showing the power transmission structureof the multipurpose work vehicle;

FIG. 3 is a perspective view showing the configuration of the vehiclebody frame;

FIG. 4 is a partial longitudinal cross-sectional side view showing thesupport structure for the engine, the HST, the transmission, the rearwheels, and other components;

FIG. 5 is a partial lateral cross-sectional plan view showing thesupport structure for the engine, the HST, the transmission, the rearwheels, and other components;

FIG. 6 is a partial plan view showing the manner in which the HST, thetransmission, and the rear axle case are connected to the engine;

FIG. 7 is a partial side view showing the manner in which the HST, thetransmission, and the rear axle case are connected to the engine;

FIG. 8 is a partial transverse cross-sectional plan view showing thestructure for transmitting power from the engine to the rear axles;

FIG. 9 is a partial transverse cross-sectional plan view showing thestructure for transmitting power from the engine to the transmission;

FIG. 10 is a partial transverse cross-sectional plan view showing theconfiguration of the transmission;

FIG. 11 is a partial longitudinal cross-sectional side view showing thestructure for transmitting power from the engine to the rear axles;

FIG. 12 is a partial transverse cross-sectional plan view showing theoperational structure of the transmission;

FIG. 13 is a partial longitudinal cross-sectional side view showing theoperational structure of the transmission;

FIG. 14 is a partial transverse cross-sectional plan view showing theconfiguration of the power take-off device;

FIG. 15 is a partial longitudinal cross-sectional side view showing theoperational structure of the power take-off device;

FIG. 16 is a partial plan view showing the configuration of the rearsuspension;

FIG. 17 is a partial side view showing the configuration of the rearsuspension;

FIG. 18 is a partial longitudinal cross-sectional rear view showing theconfiguration of the rear suspension; and

FIG. 19 is a partial side view showing the configuration of theload-carrying platform.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment in which the power transmission structure for a workvehicle according to the present invention is applied to a multipurposework vehicle, which is an example of a work vehicle, will be describedhereinbelow as an example of a preferred embodiment for carrying out thepresent invention, with reference to the drawings.

FIG. 1 is an overall side view of a multipurpose work vehicle. FIG. 2 isa schematic plan view showing the power transmission configuration ofthe multipurpose work vehicle. The multipurpose work vehicle comprises apair of left and right front wheels 2, a bottom cover 3 that doubles asa front fender, a hood 4, and other components installed on the front ofa vehicle body frame 1, as shown in these drawings. In the longitudinalmiddle of the vehicle body frame 1, a steering wheel 5 for steering thefront wheels, a sofa-style seat 6, and other components are provided toform a cab 7. At the rear of the vehicle body frame 1 are installed anengine 8, a hydrostatic transmission (hereinafter abbreviated as HST) 9as the primary transmission apparatus, a transmission 10 as a secondarytransmission apparatus, an auxiliary frame 11 for supporting thesecomponents, a pair of left and right rear wheels 12, a load-carryingplatform 13 capable of dump-swinging, and other components.

The vehicle body frame 1 is configured with a protective frame 15 or thelike that forms a cab space and that is connected to a base frame 14, asshown in FIG. 1 and FIGS. 3 through 5. The base frame 14 is configuredfrom a pair of left and right side members 14A, a plurality of crossmembers 14B that connect the side members, and other components. Theleft and right side members 14A are bent so that the front sides arepositioned below the cab 7, and the rear sides are positioned behind theseat 6. The protective frame 15 is configured from a pair of left andright side frames 15A formed in the shape of a closed loop, a pluralityof cross members 15B connecting the side frames, and other components.

In this multipurpose work vehicle, power from the engine 8 istransmitted to the HST 9, the power reduced by the HST 9 is transmittedto the transmission 10, and the power reduced by the transmission 10 isdivided in the transmission 10 into power for driving the rear wheelsand power for driving the front wheels, as shown in FIGS. 1, 2, and 4through 14.

The power for driving the rear wheels is transmitted to the left andright rear wheels 12 via a rear wheel differential device 17 providedwithin a transmission case 16, which is a casing for the transmission10, and also via a pair of left and right rear axles 18.

The power for driving the front wheels is configured by a front wheelpower take-off device 19 connected to and installed on the lower rightfront of the transmission case 16, a first power transmission shaft 20capable of expanding and contracting, a second power transmission shaft21, a differential device 22 for the front wheels, a pair of left andright third power transmission shafts 23, a pair of left and right frontaxles (not shown), a plurality of universal couplings 24 that connectthese components together, and other components.

The left and right front wheels 2 are supported via the front axles (notshown) or the like on front axle cases 26, which are independentlysuspended on the vehicle body frame 1 via a front suspension 25, asshown in FIGS. 1 and 2. A strut type independent suspension is used asthe front suspension 25. The left and right front axle cases 26 have wetmultidisk brakes 27 installed as front wheel brakes in their interiors.

The left and right rear wheels 12 are supported on the transmission case16 and on a pair of left and right rear axle cases 27 that extendoutward to the left and right from the transmission case 16, via thedifferential device 17 for the rear wheels, the rear axles 18, and othercomponents, as shown in FIGS. 1, 2, and 4 through 10. The left and rightrear axle cases 27 are supported on the auxiliary frame 11 along withthe engine 8, the HST 9, the transmission 10, and other components. Discbrakes 28 are installed as rear wheel brakes on the protruding ends ofthe left and right rear axle cases 27.

The auxiliary frame 11 is configured from a pair of left and right sidemembers 11A bent into L shapes, a plurality of cross members 11B thatconnect the side members, a first plate 11C for supporting the engine, apair of left and right second plates 11D for supporting the rear axlecases, a pair of left and right holders 11E for holding the left andright rear axle cases 27 in place, and other components, as shown inFIGS. 4, 5, and 15 through 18. The left and right holders 11E are placedadjacent to the corresponding side members 11A farther inward in thevehicle body. The auxiliary frame 11 is suspended on the vehicle bodyframe 1 via a rear suspension 29. A five-linkage type rigid axlesuspension is used as the rear suspension 29.

The engine 8 is mounted in a lateral orientation on the first plate 11Cof the auxiliary frame 11 so that an output shaft 31 that rotatesintegrally with a flywheel 30 of the engine lies along the left andright width direction of the vehicle body, and that an end plate 32 ofthe engine is coplanar with the outer right side of the vehicle body, asshown in FIGS. 1, 2, and 4 through 11. An output gear 33 is fitted usinga spline to the output shaft 31.

The HST 9 is configured with a hydraulic pump 35, a primary hydraulicmotor 36, a secondary hydraulic motor 37, and other components providedwithin a housing 34 of the HST. The housing 34 is configured from a portblock 34A, a first case 34B that covers the hydraulic pump 35, a secondcase 34C that covers the primary hydraulic motor 36, a third case 34Dthat covers the secondary hydraulic motor 37, and other components. Anaxial plunger type variable capacity pump is used as the hydraulic pump35. An axial plunger type constant capacity motor is used as the primaryhydraulic motor 36. An axial plunger type variable capacity motor isused as the secondary hydraulic motor 37.

The placement of the HST 9 is designed so that a pump shaft 38 as aninput shaft thereof and a motor shaft 39 as an output shaft thereof liealong the left and right width direction of the vehicle body.

The hydraulic pump 35 has an inclined plate 35A that is operativelyconnected via a hydraulic servo mechanism (not shown) to a neutraltwo-way gear-change pedal (not shown) provided in the cab 7. Thehydraulic servo mechanism is configured so as to tilt the inclined plate35A of the hydraulic pump 35 on the basis of the depression of thegear-change pedal, wherein the inclined plate is tilted up to an anglecorresponding to the amount by which the gear-change pedal is depressed.In other words, the gear-change operation of the HST 9 via the tiltingof the pump inclined plate 35A can be performed by depressing thegear-change pedal.

In the secondary hydraulic motor 37, an inclined plate 37A is urged backinto the neutral position by a pressure spring 40, and is tilted againstthe urging of the pressure spring 40 by the action of a piston 41. Thepiston 41 is connected to an oil supply passage (not shown) thatsupplies hydraulic fluid from the hydraulic pump 35 to the primaryhydraulic motor 36 and the secondary hydraulic motor 37. The internalpressure of the oil supply passage varies in accordance with fluctuationin the travelling load. When the internal pressure of the oil supplypassage exceeds a specific value due to an increase in the travellingload, the piston 41 tilts the inclined plate 37A of the secondaryhydraulic motor 37 against the urging of the pressure spring 40 up to anangle of inclination at which the internal pressure of the oil supplypassage is balanced with the urging force of the pressure spring 40. Inother words, in cases in which the internal pressure of the oil supplypassage exceeds a specific value due to an increase in the travellingload, the tilting of the motor inclined plate 37A results in the gearchange operation of the HST 9. When this gear change operation isperformed, the capacity of the entire hydraulic motor increases, therotational speed of the motor shaft 39 decreases, and the motor shaft 39produces a greater output torque. It is thereby possible to obtain ahigh output torque corresponding to the increase in the travelling load.

In cases in which the travelling load further increases and the internalpressure of the oil supply passage rises after the inclined plate 37A ofthe secondary hydraulic motor 37 has been tilted to the angle limit dueto the increase in the travelling load, the internal pressure of the oilsupply passage acts as reactive force that pushes the inclined plate 35Aof the hydraulic pump 35 back towards the neutral position. Therotational speed of the motor shaft 39 can thereby be reduced further,and a higher output torque corresponding to an even higher travellingload can be obtained.

An input gear 42 that meshes with an output gear 33 of the engine 8 in amanner that enables reduced-gear power transmission is fitted using aspline to the left end of the pump shaft 38. In other words, the pumpshaft 38 of the HST 9 is connected to the output shaft 31 of the engine8 via the output gear 33 and the input gear 42. A cooling fan 43 isfitted using a spline to the right end of the pump shaft 38. An oilfilter 44 is installed in the first case 34B.

The transmission 10 is installed laterally in the auxiliary frame 11, sothat an input shaft 45 as a power transmission shaft of thetransmission, a gear-change shaft 46, a reverse shaft 47, a first outputshaft 48 for driving the rear wheels, and a second output shaft 49 fordriving the front wheels lie along the left and right width direction ofthe vehicle body, as shown in FIGS. 1, 2, and 4 through 14.

The input shaft 45 is placed at the upper front of the transmission case16, and the right end of the input shaft is fitted using a spline to themotor shaft 39 of the HST 9, as shown in FIGS. 8 through 14. A firstlow-speed gear 50, a first high-speed gear 51, and a first reverse gear52 are integrally formed on the input shaft 45.

The gear-change shaft 46 is placed in the transmission case 16 so as tobe positioned behind and below the input shaft 45. A second low-speedgear 53 that meshes with the first low-speed gear 50, a secondhigh-speed gear 54 that meshes with the first high-speed gear 51, and asecond reverse gear 55 are externally fitted and mounted on thegear-change shaft 46 in a manner that allows them to rotate relative toeach other. A first shifter 56 that rotates integrally with thegear-change shaft 46 is disposed between the second low-speed gear 53and the second high-speed gear 54 in the gear-change shaft 46. The firstshifter 56 is provided so as to be capable being slidably displacedamong a low-speed forward position where the first shifter meshes withthe second low-speed gear 53, a high-speed forward position where thefirst shifter meshes with the second high-speed gear 54, and a neutralposition where the first shifter does not mesh with either of the gears.A second shifter 57 that rotates integrally with the gear-change shaft46 is disposed at a location to the left of the second reverse gear 55in the gear-change shaft 46, and the second shifter 57 is provided so asto be capable of being slidably displaced between a reverse positionwhere the second shifter meshes with the second reverse gear 55, and aneutral position where the second shifter does not mesh with the secondreverse gear 55. A first reduction gear 58 is fitted using a spline withthe right end of the gear-change shaft 46.

The reverse shaft 47 is placed in the transmission case 16 so as to bepositioned behind and above the input shaft 45, and also above and infront of the gear-change shaft 46. A third reverse gear 59 that mesheswith the first reverse gear 52 and the second reverse gear 55 isexternally fitted and mounted to the reverse shaft 47 in a manner thatenables relative rotation.

The first output shaft 48 is placed in the transmission case 16 so as tobe positioned behind and below the gear-change shaft 46. A secondreduction gear 60 that meshes with the first reduction gear 58 is fittedusing a spline to the right end of the first output shaft 48. A piniongear 61 is formed integrally in the first output shaft 48 at a locationto the left of the second reduction gear 60. The pinion gear 61 mesheswith a ring gear 62 provided to the rear wheel differential device 17,which is positioned behind and below the pinion gear 61.

The second output shaft 49 is placed in the transmission case 16 so asto be positioned below the right front of the first output shaft 48. Apower transmission gear 63 that meshes with the second reduction gear 60is formed integrally on the left end of the second output shaft 49.

A fork rod 64 and a camshaft 65 are longitudinally aligned while lyingalong the left and right width direction of the vehicle body, at aposition that is behind the gear-change shaft 46 and above thedifferential device 17 in the transmission case 16.

A first shifting fork 66 that slides integrally with the first shifter56, and a second shifting fork 67 that slides integrally with the secondshifter 57, are externally fitted on the fork rod 64 in a manner thatallows the shifting forks to slide relative to each other.

A first guiding groove 65S into which an engaging protuberance 66Aformed integrally on the first shifting fork 66 is engageably inserted,and a second guiding groove 65B into which an engaging protuberance 67Aintegrally formed on the second shifting fork 67 is engageably inserted,are formed in the camshaft 65. The first guiding groove 65A and thesecond guiding groove 65B are formed so as to operatively guide theengaging protuberances 66A, 67A of the first shifting fork 66 and secondshifting fork 67 as the camshaft 65 rotates. The first shifter 56 andsecond shifter 57 are thereby slidably displaced via the first shiftingfork 66 and second shifting fork 67 into gear-change positions thatcorrespond to the operating position of the camshaft 65. An operatinggear 68 and a disc 69 that rotate integrally with the camshaft 65 areexternally fitted over the right end of the camshaft 65.

A sector gear 72 that fluctuates integrally with an operating arm 71 viaa coupling shaft 70 oriented left to right is meshed with the operatinggear 68. The operating arm 71 is operatively connected to a gear-changelever (not shown) provided to the cab 7.

Four through-holes 69A, which are capable of holding the camshaft 65 inthe neutral position, the low-speed forward position, the high-speedforward position, and the reverse position, are formed in the disc 69. Aball detent mechanism 73 is installed in the transmission case 16, andthis detent mechanism 73 engages with the through-holes 69A to hold thecamshaft 65 at the neutral position, the low-speed forward position, thehigh-speed forward position, and the reverse position.

In other words, by operating the gear-change lever, it is possible toswitch the gear-change state of the transmission 10 among a neutralstate in which the first shifter 56 and the second shifter 57 are bothheld in a neutral position, a low-speed forward state in which the firstshifter 56 is held in a low-speed forward position and the secondshifter 57 is held in a neutral position, a high-speed forward state inwhich the first shifter 56 is held in a high-speed forward position andthe second shifter 57 is held in a neutral position, and a reverse statein which the first shifter 56 is held in a neutral position and thesecond shifter 57 is held in a reverse position.

The differential device 17 for the rear wheels is configured from acasing 74 that rotates integrally with the ring gear 62, a support shaft75 that is installed in the casing 74 and that lies orthogonal to therear axles 18, a pair of pinion gears 76 that fits externally over bothends of the support shaft 75 and that is capable of rotating relative toeach other, a pair of left and right side gears 77 that are fittedinside the casing 74 to be capable of rotating relative to each otherand that are fitted using splines on the corresponding rear axles 18,and other components, as shown in FIGS. 8 and 10.

The transmission case 16 is equipped with a lock mechanism 78 thatprevents the rear wheel differential device 17 from causing differentialmotion between the left and right rear wheels 12 in conjunction with thedepression of a diff-lock pedal (not shown) provided in the cab 7.

The lock mechanism 78 is configured from a clutch 79 that is fittedusing a spline to the right rear axle 18 and that prevents differentialmotion, a shifting fork 80 that slides integrally with the clutch 79, aleft-to-right oriented operating shaft 81 that supports the shiftingfork 80 in a manner that allows the shifting fork 80 to rotate and slidein relative fashion, an operatively connecting pin 82 that operativelyconnects the shifting fork 80 with the operating shaft 81, an operatingarm 83 that is integrally and rotatably connected to the operating shaft81, and other components.

A camshaft 80A through which the operatively connecting pin 82 isengageably inserted is formed in the shifting fork 80. The operativelyconnecting pin 82 rotates integrally with the operating shaft 81. Theoperating arm 83 is operatively connected to the diff-lock pedal. Thecamshaft 80A is formed so that the shifting fork 80 is slidablydisplaced in conjunction with the rotation of the operatively connectingpin 82, whereby the clutch 79 is slidably displaced between a lockedposition of being interlocked with the casing 74 of the differentialdevice 17, and a lock-releasing position where the interlocking isreleased.

The power take-off device 19 for the front wheels is configured from afront wheel power take-off clutch 34 that is fitted using a spline onthe right end of the second output shaft 49, a first bevel gear 85 thatfits externally over the second output shaft 49 in a manner that allowsrelative rotation, a power take-off shaft 87 on which a second bevelgear 86 that meshes with the first bevel gear 85 is formed integrally, acasing 88 connected to the transmission case 16 so as to cover thesecomponents, and other components, as shown in FIGS. 14 and 15.

The casing 88 of the power take-off device 19 is provided with a driveswitching mechanism 89 that switches between a four-wheel drive state inwhich the clutch 84 is interlocked with the first bevel gear 85, and atwo-wheel drive state in which the interlocking of the clutch 84 withthe first bevel gear 85 is released, in conjunction with the operationof a switching lever (not shown) provided in the cab 7.

The drive switching mechanism 89 is configured from a verticallyoriented operating shaft 90 that is supported on the casing 88 and thatis capable of relative rotation, an operating arm 91 that is integrallyand rotatably connected to the operating shaft 90, and other components.An eccentric cam 92 is integrally formed on the lower end of theoperating shaft 90, and this eccentric cam 92 slidably displaces theclutch 84 between a power transmission position where the clutch isinterlocked with the first bevel gear 85, and a non-power transmissionposition where the interlocking is released, in conjunction with therotation of the operating shaft 90. The operating arm 91 is operativelyconnected to a switching lever.

The transmission case 16 is configured from a left-side first case 93and a right-side second case 94, and these two cases are connected,thereby forming a housing space for housing the transmission 10 and thedifferential device 17 for the rear wheels, as shown in FIGS. 2, 4through 12, and 14. A protrusion 94A that protrudes from an input unit10A of the transmission 10 towards an output unit 8A of the engine 8 isintegrally formed on the second case 94. The protrusion 94A is formed soas to have a first case portion 94Aa that covers the flywheel 30, theoutput gear 33, and other components provided to the engine 8; a secondcase portion 94Ab that covers the input gear 42 and other componentsprovided to the pump shaft 38; and a third case portion 94Ac that coversthe primary hydraulic motor 36 of the HST 9.

The left end edge of the protrusion 94A is a peripheral edge 94 a of thefirst case portion 9Aa, and this peripheral edge 94 a is connected tothe end plate 32 of the engine 8. The right end edge of the protrusion94A is a peripheral edge 94 b of the second case portion 94Ab, and thisperipheral edge 94 b and a peripheral edge 94 c of the third caseportion 94Ac are connected to the port block 3 of the HST 9 via a gasket95.

The pump side of the port block 34A of the HST 9 is thereby connected tothe end plate 32 of the engine 8 via the first case portion 94Aa and thesecond case portion 9 b of the transmission case 16, and the motor sideof the port block 3 is connected to the input unit 10A of thetransmission 10 via the third case portion 94Ac of the transmission case16, so that the port block 34A extends between the engine 8 and thetransmission 10.

In other words, with this configuration, the second case 94 of thetransmission case 16 is also used as the second case 34C of the HST 9.The port block 34A of the HST 9 also serves as the right side wall ofthe transmission case 16, forming a housing space for housing the inputgear 42 and other components between the transmission case 16 and thesecond case 94. The structural components of the HST 9 and thetransmission case 16 can thereby be reduced.

Moreover, since the protrusion 9 of the second case 94 in thetransmission case 16 serves as a connecting member for connecting theengine 8 and transmission 10, the configuration can be simplified andcosts can be reduced by reducing the number of components, in comparisonwith cases in which a special connecting member is provided.

Furthermore, since the port block 34A of the HST 9 functions as areinforcing member for reinforcing the protrusion 94A of the second case94 that connects the engine 8 to the transmission 10, the strength ofthe connection between the engine 8 and the transmission 10 can beimproved without providing a special reinforcing member.

With this power transmission structure, as previously described, theoutput shaft 31 of the engine 8, the pump shaft 38 and motor shaft 39 ofthe HST 9, and the power transmission shafts 45 to 49 of thetransmission 10 are disposed in a left-to-right orientation whileparallel to the left and right rear axles 18. The output shaft 31 of theengine 8, the pump shaft 38 and motor shaft 39 of the HST 9, and thepower transmission shafts 45 to 49 of the transmission 10 can thereby bedisposed so as to have small longitudinal intervals between thesecomponents. With this type of arrangement, the engine 8, the HST 9, andthe transmission 10 can be placed in a manner that reduces their lengthsin the longitudinal direction (or fore-and-aft direction) of the vehiclebody. The transmission 10 can also be configured in a manner thatreduces the length of the transmission in the longitudinal direction ofthe vehicle body. As a result, the entire length of the vehicle body canbe reduced.

By connecting the pump shaft 38 of the HST 9 to the output shaft 31 ofthe engine 8, and the motor shaft 39 of the HST 9 to the input shaft 45of the transmission 10, the HST 9 can be disposed to the right of thelaterally oriented engine 8 and transmission 10 so that, when viewedfrom the side, the HST 9 overlaps the engine 8 and transmission 10. Theentire length of the vehicle body can thereby be reduced in comparisonwith cases in which the engine 8, the HST 9, and the transmission 10 arealigned in a row along the longitudinal direction of the vehicle body.

Moreover, by placing the power transmission shafts 45 to 49 of thetransmission 10 in a left-to-right orientation parallel to the left andright rear axles 18, flat gears that are less expensive than bevel gearscan be used as the pinion gear 61 and the ring gear 62, which areinstalled as final gears that connect the first output shaft 48 of thetransmission 10 with the left and right rear axles 18 in a manner thatenables power transmission.

The rear suspension 29 is configured from a pair of left and right upperarms 96 and a pair of left and right lower arms 97 for positioning theleft and right rear wheels 12 with respect to the longitudinal directionof the vehicle body; a single lateral rod 98, a pair of left and rightdampers 99, and a pair of left and right coil springs 100, forpositioning the left and right rear wheels 12 with respect to theleft-to-right direction of the vehicle body; and other components, asshown in FIGS. 1, 3 through 5, and 16 through 18.

The left and right upper arms 96 and the left and right lower arms 97are disposed in a longitudinal orientation so as to be positioneddirectly below the side members 14A of the base frame 14. Connectingbosses 96A, 96B, 97A, 97B are integrally mounted on both ends of theleft and right upper arms 96 and lower arms 97.

The front bosses 96A in the left and right upper arms 96 are connected,via rubber bushes 101, left-to-right oriented bolts 102, and the like,to brackets 14C provided at the rear parts of the left and right sidemembers 14A in the base frame 14. The rear bosses 96B are connected, viarubber bushes 101, left-to-right oriented bolts 102, and the like, tobrackets 11F provided at the top ends of the corresponding side members11A in the auxiliary frame 11.

The front bosses 97A in the left and right lower arms 97 are connected,via rubber bushes 101, left-to-right oriented bolts 102, and the like,to brackets 14D provided at the longitudinal middles of the left andright side members 14A in the base frame 14. The rear bosses 97B areconnected, via rubber bushes 101, left-to-right oriented bolts 102, andthe like, to brackets 11G provided at the front ends of thecorresponding side members 11A in the auxiliary frame 11.

The left and right upper arms 96 and the left and right lower arms 97are set so that the left and right lower arms 97 are longer than theleft and right upper arms 96, that the left and right upper arms 96 arepositioned farther to the rear of the vehicle body than the left andright lower arms 97, and that the angles of the left and right upperarms 96 in relation to the vehicle body frame 1 are greater than theangles of the left and right lower arms 97 in relation to the vehiclebody frame 1.

A lateral rod 98 is disposed in a left-to-right orientation at aposition in the vehicle body that is farther inward than the rear end ofthe base frame 14, Connecting bosses 98A, 98B are integrally mounted atboth ends of the lateral rod 98. The left boss 98A is connected, via arubber bush 103, a longitudinally oriented bolt 104, and the like, to abracket 14E provided at the rear end of the left side member 14A in thebase frame 14. The right boss 98B is connected, via a rubber bush 103, alongitudinally oriented bolt 104, and the like, to a bracket 11Hprovided at the top end of the right side member 11A in the auxiliaryframe 11.

Connecting bosses 99A, 99B are integrally mounted on both ends of theleft and right dampers 99. The top bosses 99A are connected, via rubberbushes 105, longitudinally oriented bolts 106, and the like, to brackets14F that project into the vehicle body in the rear parts of the sidemembers 14A in the base frame 14. The bottom bosses 99B are connected tocorresponding holders 11E in the auxiliary frame 11 via rubber bushes105, longitudinally oriented bolts 106, and the like. Coil springs 100are externally fitted over the dampers 99 so that shocks from the roadare absorbed by the coil springs 100, and that the movement of the coilsprings 100 is controlled by the dampers 99 (periodic vibrations of thecoil springs 100 converge sooner).

In other words, the rear suspension 29 is configured so that the leftand right upper arms 96 and lower arms 97 overlap with the left andright side members 11A of the base frame 14 as seen in a plan view, thelateral rod 98 is disposed at the rear end part which is farther inwardin the vehicle body than the rear end of the base frame 14, and the leftand right dampers 99 and coil springs 100 are placed adjacent to thecorresponding side members 14A of the base frame 14 and are positionedfarther inward in the vehicle body than the left and right side members14.

It is thereby possible to avoid problems wherein other objects easilycome into contact with the rear suspension 29 as a result of the rearsuspension 29 protruding out from the base frame 14 to the side of thevehicle body, and it is also possible to ensure that a large space isformed between the base frame 14 and the auxiliary frame 11 suspended onthe base frame 14 via the rear suspension 29. As a result, damage to therear suspension 29 as a result of contact with other objects can beeffectively prevented. The engine 8, the HST 9, the transmission 10, andother components can also be installed in the auxiliary frame 11 in asuitable manner in which there is enough space from the base frame 14and other components. It is thereby possible to preemptively preventproblems in which the engine 8, the HST 9, the transmission 10, andother components come into contact with the base frame 14 and othercomponents when the rear suspension 29 reduces vibrations or shocks fromthe road.

If, for example, the engine 8, the HST 9, and the transmission 10 areinstalled in the base frame 14, and the left and right rear wheels 12are suspended on the base frame 14 via the rear suspension 29, then theleft and right rear wheels 12 are displaced in relation to the engine 8,the HST 9, and the transmission 10 when the rear suspension 29 reducesvibrations or shocks from the road. Therefore, universal couplings orthe like that allow the left and right rear wheels 12 to be displaced inrelation to the engine 8, the HST 9, and the transmission 10 must beinstalled in the system for transmitting power to the left and rightrear wheels 12.

By contrast, the engine 8, the HST 9, and the transmission 10 aremounted together with the left and right rear wheels 12 in the auxiliaryframe 11 suspended on the base frame 14 via the rear suspension 29 inthis multipurpose work vehicle. The engine 8, the HST 9, and thetransmission 10 can thereby be displaced integrally together with theleft and right rear wheels 12 in relation to the base frame 14 when therear suspension 29 reduces vibrations or shocks from the road.Therefore, universal couplings or the like that allow the left and rightrear wheels 12 to be displaced in relation to the engine 8, the HST 9,and the transmission 10 do not need to be installed in the system fortransmitting power to the left and right rear wheels 12.

In other words, the power transmission structure can be simplified andcosts can be reduced by reducing the number of components throughplacement of the engine 8, the HST 9, and the transmission 10 togetherwith the left and right rear wheels 12 in the auxiliary frame 11suspended on the base frame 14 via the rear suspension 29.

Moreover, rubber bushes 101, 103, 105 are placed between the base frame14 and the rear suspension 29 and also between the auxiliary frame 11and the rear suspension 29, whereby twisting to the left and right canbe absorbed by these rubber bushes 101, 103, 105. As a result, aninexpensive rigid axle suspension with a simple structure can be used asthe rear suspension 29, and a smoother ride can be provided.

Since the engine 8 is supported in a vibration-proof manner on the baseframe 14 via the rear suspension 29, vibration from the engine 8 can beprevented from reaching the base frame 14 without providing anyengine-specific anti-vibration rubber components. Moreover, in cases inwhich engine-specific anti-vibration rubber components are provided, thepower transmission system running from the engine 8 to the transmission10 must be provided with hydraulic couplings or the like for allowingrelative displacement therein, but no such universal couplings or thelike are needed in this multipurpose work vehicle. In other words, theconfiguration can be further simplified and costs further reduced byreducing the number of components, and an even smoother ride can beensured.

A pair of left and right brackets 107 is installed on the bottom of theload-carrying platform 13 at a position that is behind the longitudinalmiddle, as shown in FIG. 19. The left and right brackets 107 areexternally fitted over left-to-right oriented support shafts 108provided at the rear ends of the base frame 14 in a manner that allowsthe brackets 107 to rotate relative to each other. Four rubber mounts109 that are secured and supported by the base frame 14 are installed onthe bottom of the load-carrying platform 13. A pair of left and rightswinging links 110 is connected at one end to the longitudinal middle inthe bottom of the load-carrying platform 13. Long holes 110A are formedat the other ends of the left and right swinging links 110, andleft-to-right oriented stopping pins 111 provided at the rear of thebase frame 14 are engageably inserted through these long holes 11A.Handles 112 are installed on the left and right sides at the front ofthe load-carrying platform 13.

Specifically, by grasping the handles 112 and pulling up the front sideof the load-carrying platform 13, it is possible to switch the positionof the load-carrying platform 13 from a carrying position in which therubber mounts 109 are secured and supported by the base frame 14, to adumping position in which the rubber mounts 109 are raised above thebase frame 14 and in which the support shafts 108 come into contact withthe front edges of the long holes 110A in the swinging links 110.

Concavities 110B that can engage with the stopping pins 111 are formedso as to recess upwards at the front ends of the long holes 110A in theswinging links 110.

Specifically, when the load-carrying platform 13 is switched to thedumping position, the concavities 110B engage with the support shafts108 that have come into contact with the front edges of the long holes110A, whereby the load-carrying platform 13 can be held at the dumpingposition. The position of the load-carrying platform 13 can be switchedfrom dumping to carrying by grasping the handles 112 and releasing theengagement between the concavities 110B of the swinging links 110 andthe stopping pins 111.

The transmission 10 is equipped with a detection mechanism 113 fordetecting the neutral state of the transmission 10, as shown in FIG. 13.The detection mechanism 113 is configured from a neutral detectionconcavity 69B formed by recessing the external periphery of the disc 69that rotates integrally with the camshaft 65, and a switch 114 that isswitched to a closed state by the engageable insertion of an actuator114A into the concavity 69B.

The switch 114 is a structural element of a startup restraint circuit(not shown) that restrains the engine 8 from starting up. The startuprestraint circuit is configured so as to prevent the engine 8 fromstarting up in cases in which the switch 114 is open; i.e., in cases inwhich the transmission 10 is in neutral.

Other Embodiments

[1] The work vehicle may be a tractor, a lawn mower, a rice-plantingmachine, or the like.

[2] The work vehicle may be configured as a four-wheel drive vehicle inwhich the engine 8 and the transmission devices 9, 10 are placed in thefront of the vehicle body, and the power from the engine 8 istransmitted via the transmission devices 9, 10 to the left and rightfront wheels 2 and the left and right rear wheels 12.

[3] The work vehicle may be configured as a rear-wheel drive vehicle inwhich the engine 8 and the transmission devices 9, 10 are placed in therear of the vehicle body, and the power from the engine 8 is transmittedvia the transmission devices 9, 10 to the left and right rear wheels 12.

[4] The work vehicle may be configured as a front-wheel drive vehicle inwhich the engine 8 and the transmission devices 9, 10 are placed in thefront of the vehicle body, and the power from the engine 8 istransmitted via the transmission devices 9, 10 to the left and rightfront wheels 2.

[5] The transmission devices may include only the transmission 10, abelt-type continuously variable transmission instead of the HST 9, or ahydromechanical transmission (HMT) composed of the HST 9 and a planetarygear-type continuously variable transmission.

[6] A transmission that does not include the secondary hydraulic motor37 may be used for the EST 9.

[7] A five-linkage type rigid axle suspension may be used as the frontsuspension 25; and an auxiliary frame 11 comprising the left and rightfront wheels 2, the engine 8, the transmission devices 9, 10, and othersuch components may be suspended via this front suspension 25 on thevehicle body frame 1.

[8] The engine 8 and the transmission devices 9, 10 may be installed inthe auxiliary frame 11 so that the shafts 31, 38, 39, and 45 to 49thereof are oriented longitudinally.

[9] The engine 8 and the transmission devices 9, 10 may be connected soas to be capable of power transmission via power transmission shafts,power transmission belts, and other such components.

[10] The five-linkage type rigid axle suspension used as the frontsuspension 25 or the rear suspension 29 may be designed so that eitherthe left and right upper arms 96 are longer than the left and rightlower arms 97, or the upper and lower arms are equal in length. Thesuspension may also be designed so that either the left and right upperarms 96 are positioned farther forward in the vehicle body than the leftand right lower arms 97, or positions thereof in the longitudinaldirection of the vehicle body are the same. Furthermore, the suspensionmay be designed so that either the angles of the left and right upperarms 96 in relation to the vehicle body frame 1 are less than the anglesof the left and right lower arms 97 in relation to the vehicle bodyframe 1, or the angles of the upper and lower arms in relation to thevehicle body frame 1 are equal.

[11] The five-linkage type rigid axle suspension used as the frontsuspension 25 or the rear suspension 29 may be designed so that theright boss 98B in the lateral rod 98 is connected via a rubber bush 103,a longitudinally oriented bolt 104, and the like to the bracket 14Eprovided at the rear end of the right side member 14A in the base frame14, and the left boss 98A in the lateral rod 98 is connected via arubber bush 103, a longitudinally oriented bolt 104, or the like to thebracket 11H provided at the top of the left side member 11A in theauxiliary frame 11. Either one of the left and right bosses 98A, 98B ofthe lateral rod 98 connected to the bracket 11H provided to theauxiliary frame 11 may be connected via a rubber bush 103, alongitudinally oriented bolt 104, or the like to a bracket provided tothe transmission case 16, the rear axle case 27, or the like installedon the auxiliary frame 11, instead of being connected to the bracket 11Hof the auxiliary frame 11.

[12] The configuration of the auxiliary frame 11 can have variousmodifications in accordance with the installation placement of theengine 8 and the transmission devices 9, 10; the structure forconnecting the engine 8 and the transmission devices 9, 10; the type ofinstalled transmission devices 9, 10; the configuration of thefive-linkage type rigid axle suspension used as the front suspension 25or the rear suspension 29; or the like.

[13] A five-linkage type rigid axle suspension may be used as the frontsuspension 25.

[14] The link rigid axle suspension used for the suspension 25 or 29 maybe a three-link suspension comprising a pair of left and right arms 97,a lateral rod 98, a pair of left and right coil springs 100, and a pairof left and right dampers 99.

[15] The configuration may be designed so that the transmission 10 issuspended along with the left and right front wheels 2 or the left andright rear wheels 12 on the vehicle body frame 1 via the frontsuspension 25 or the rear suspension 29.

[16] The configuration may be designed so that the transmission 10 andthe HST 9 are suspended along with the left and right front wheels 2 orthe left and right rear wheels 12 on the vehicle body frame 1 via thefront suspension 25 or the rear suspension 29.

[17] The configuration may be designed so that the engine 8 and thetransmission devices 9, 10 are suspended along with the left and rightfront wheels 2 or the left and right rear wheels 12 on the vehicle bodyframe 1 via the front suspension 25 or the rear suspension 29.

1. A work vehicle comprising: a pair of left and right wheels; a vehiclebody frame supported at least partially by the pair of left and rightwheels; and a suspension provided between the pair of left and rightwheels and the vehicle body frame, the suspension being a five-linkagetype rigid axle suspension including: a pair of left and right upperarms and a pair of left and right lower arms for positioning the pair ofleft and right wheels in the longitudinal direction of the vehicle body;a lateral rod for positioning the pair of left and right wheels in thelateral direction of the vehicle body; a pair of left and right coilsprings for absorbing shocks from the road; a pair of left and rightdampers for controlling the movements of the pair of left and right coilsprings; and an auxiliary frame for supporting the pair of left andright wheels, an engine, and a transmission device, wherein theauxiliary frame is suspended on the vehicle body frame via thesuspension.
 2. The work vehicle of claim 1, wherein the vehicle bodyframe has a left side member and a right side member; the left upper armis disposed at a position that substantially overlaps with the left sidemember as seen in a plan view; and the right upper arm is disposed at aposition that substantially overlaps with the right side member as seenin a plan view
 3. The work vehicle of claim 2, wherein the left lowerarm is disposed at a position that substantially overlaps with the leftside member as seen in a plan view; and the right lower arm is disposedat a position that substantially overlaps with the right side member asseen in a plan view.
 4. The work vehicle of claim 1, wherein the pair ofleft and right dampers and the pair of left and right coil springs aredisposed inwardly of the left and right side members.